A known problem in shaping technology is that considerable stresses occur in the sheet metal material due to punching, embossing, deep drawing, etc., so that the shape of the finished part is predictable only in combination with numerous empirical values and/or highly complex computation methods.
If a punched part (referred to hereinafter as the main structure) does not contain any holes or other recesses (referred to below as minor structures), then the spatial position of these minor structures with respect to the main structure is usually controllable only with a great loss of quality.
It is particularly difficult to implement the geometric and positional tolerance of minor structures in a punched part if the thickness of the sheet metal is great in relation to a degree of shaping. In other words, in the case of a shell-shaped part having an inside diameter of 200-300 mm, for example, the sheet metal is bent almost at a right angle and the thickness of the sheet metal here amounts to approximately 4-6 mm, so considerable deformation of the sheet metal may be expected in the shaping area. This deformation means that the shape of minor structures previously created in the sheet metal may be distorted and thus they may not have a high geometrical and positional accuracy.
Shaping sheet metal to yield a pump shell of a torque converter is a particular problem. The pump shell here is the housing part of a torque converter which accommodates the pump blades. This pump shell has a wall thickness of 5 mm, for example, and an inside diameter of 240 mm. With these dimensions, the rated torque is approximately 300 Nm. To accommodate the pump blades, embossed slots are provided in the inside surface of the pump shell so that the pump blades are then inserted into the slots and soldered there. In order for the blades to have a high positional accuracy, they are mostly guided via three embossed slots in the area of the surfaces of the pump shell. For the plurality of blades in the pump shell, this results in annular rows of embossed slots near the axis of rotation, approximately at the most elevated point in the shell and very close to the outside diameter. To achieve a high precision for the position and shape of the embossed slots, these slots have in the past been introduced into the completely punched shell form via a special machine (called a copy machine). With this special machine, at least one ram, i.e. a stamping device, is directed radially at the inside surface of the pump shell. A corresponding counter-die is oriented with the outside surface of the pump shell at the particular location. By embossing the embossed slots on the inside of the pump shell in cycles with subsequent advancing of the workpiece to the next embossing position, a row of embossed slots is manufactured. For example, when there are 31 pump blades, these slots must be embossed 31 times and then the workpiece must be turned. Even if the special machine mentioned is able to punch all three “rings” of embossed slots simultaneously, 31 cycles are nevertheless required to produce them in this example.